Watching Hydrogens Migrate: Step by Step from [ReI(η6‑C6H6)2]+ to [ReIII(η3‑C6H9)(η6‑C6H6)(NCCH3)2]2

• Published in: Inorganic chemistry 2022-02, Vol.61 (8), p.3683-3689
• Main Authors: Siebenmann, Lukas, Bolliger, Robin, Braband, Henrik, Blacque, Olivier, Alberto, Roger
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.1c03811

Arene substitution reactions in [M­(η6-arene)2]0/2+ are well documented for Groups 6 and 8 but are essentially unknown for the manganese triad. Aiming to replace benzene in [ReI(η6-C6H6)2]+, we altered the hapticity of one coordinated benzene, which we found to be tunable stepwise from an η6 to an η3-allyl coordination mode. Reduction of [ReI(η6-C6H6)2]+ with hydrides gives [ReI(η5-C6H7)­(η6-C6H6)]. Subsequent addition of acid yields [ReIIIH­(η5-C6H7)­(η6-C6H6)]+, which converts to [ReI(η4-C6H8)­(η6-C6H6)­NCCH3]+ in acetonitrile. Further protonation gives the title complex [ReIII(η3-C6H9)­(η6-C6H6)­(NCCH3)2]2+ by a rhenium-mediated, intramolecular hydride shift. Herein, we present a full mechanistic elucidation of these transformations based on NMR studies, isolation of reaction intermediates, and their full characterizations. The structural feature {ReIII(η6-C6H6)} is unprecedented. Direct arene exchange from [ReI(η6-C6H6)2]+ to [ReI(η6-arene)­(η6-C6H6)]+ was found only under strongly acidic conditions in neat arene. The analogous chemistry of the lighter homologue technetium (99Tc) is distinctly different. Treatment of [TcI(η5-C6H7)­(η6-C6H6)] with acid in acetonitrile yields only mixtures of [TcI(η6-C6H6)2]+ and [TcII(NCCH3)6]2+.